1. Field of the Invention
The present invention relates to a piezoelectric driven type vibratory feeder.
2. Description of the Related Art
As a first example of a piezoelectric driven type vibratory feeder, a device, such as that illustrated in FIG. 15, is disclosed in Japanese Patent No. 2762211. A transporting member 5 (term used in the specification, and will be used below) is supported by transporting member supporting members 8, which are a pair of front and back vertical spring steel members. The lower end portions of the transporting member supporting members 8 are secured to a base 3. The heights of the front and back portions of the base 3 are different. In other words, the base 3 has a trapezoidal shape. Therefore, the spring operating lengths of the transporting member supporting members 8 differ at the front and back sides of the base 3. A pair of front and back vibration members 9 are secured to the bottom surface of the transporting member 5, and comprise corresponding piezoelectric devices 1 bonded to both surfaces of corresponding elastic plates 2. Accordingly, the piezoelectric driven type vibratory feeder has what is called a bimorph structure. Mass members 7 and 7 having different masses are mounted to the lower ends of the corresponding elastic plates 2. Transportation parts 6 are to be transported on the transporting member 5 in the direction of an arrow. When an alternating voltage is applied to the piezoelectric devices 1, the piezoelectric devices 1 bonded to both surfaces of their corresponding elastic plates 2 expand and contract. By the expansion and contraction of the piezoelectric devices 1, the transporting member 5 vibrates in an oblique direction, so that the transportation parts 6 are, as conventionally known, transported in the direction of the arrow.
In such a piezoelectric driven type vibratory feeder, however, since the mass members 7 and 7 are secured to the lower ends of their corresponding elastic plates 2, and the transporting member 5 is secured to the bases of the elastic plates 2, rotational motion occurs around the secured points as indicated by the double-headed arrows. This causes rotational motion of the transporting member 5, which may be very complicated. In addition, a common alternating voltage is applied. Therefore, since the masses of the mass members 7 and 7 are different, even if the spring constants of the elastic plates 2 are the same, the resonant frequencies of these two vibratory systems are different. Consequently, the amplitudes of the mass members 7 and 7 are different, and, with regard to their vibration displacements, the alternating voltages applied to the mass members 7 and 7 are out of phase. Thus, the transporting member 5 may vibrate in a more complicated manner, so that a smooth transportation operation may not be performed over the entire transporting member 5.
FIG. 16 illustrates a second conventional example of a piezoelectric driven type vibratory feeder disclosed in Japanese Patent Examined Publication HEI02-50806 B2. By bolts b, ends of an obliquely provided pair of front and back plate springs 13a and 13b are secured, one at each end of a plate-spring-mounting block 12 secured to the bottom surface of a trough 11. By corresponding plate-spring-mounting blocks 14a and 14b, the bottom end portions of the plate springs 13a and 13b are secured to the top ends of their corresponding piezoelectric-device-mounting plate springs 15a and 15b disposed below the plate springs 13a and 13b. The bottom end portions of the piezoelectric-device-mounting plate springs 15a and 15b are secured to a base 17. Piezoelectric devices 16a and 16axe2x80x2 and piezoelectric devices 16b and 16bxe2x80x2 are bonded to both surfaces of the plate springs 15a and 15b, respectively. Alternating voltages are applied to the piezoelectric devices 16a and 16axe2x80x2 and the piezoelectric devices 16b and 16bxe2x80x2, so that the plate springs 15a and 15b bend. The trough 11 amplifies vibration by the upper plate springs 13a and 13b. Even in this conventional example, a vibration-proof structure is not provided. Therefore, from the bottom end portions of the lower plate springs 15a and 15b, a reaction force resulting from the vibration of the tough 11 or a bending reaction force of the plate springs 15a and 15b is directly transmitted to the base 17, so that, not only are other similar vibration mechanisms mounted to a common installation base Q adversely affected, but also noise is produced by a reaction force that is transmitted through the floor. In order to overcome these problems, a vibration-proof structure, such as that shown in FIG. 17, can be provided. In FIG. 17, corresponding parts to those shown in FIG. 16 are given the same reference numerals, and are not described in detail below. In the piezoelectric driven type vibratory feeder having the vibration-proof structure, a vibration-proof block 18 is mounted below the base 17, and is joined to an installation base 19 by a pair of front and back vibration-proof springs 20a and 20b having small spring constants. By this structure, the vibration reaction force transmitted to the base 17 is virtually not transmitted to the installation base 19 due to deflection of the vibration-proof springs 20a and 20b. In such a structure, however, the height of the entire piezoelectric driven type vibratory feeder becomes large. Therefore, a problem concerning the relationship with other devices disposed near the piezoelectric driven type vibratory feeder for proper arrangement therewith and a problem of a lack of stability of the piezoelectric driven type vibratory feeder arise.
In view of the above-described problems, it is an object of the present invention to provide a piezoelectric driven type vibratory feeder whose working mass member vibrates stably over the entire area of the working mass member and which can prevent a reaction force from being transmitted to an installation base or a base without increasing the height of the entire piezoelectric driven type vibratory feeder.
To this end, according to a basic form of the present invention, there is provided a piezoelectric driven type vibratory feeder comprising a base; a plurality of first plate springs, with a lower end portion of each of the plurality of first plate springs being secured to the base; a working mass member connected to an upper end portion of each of the plurality of first plate springs, and supported at the base so that the working mass member can vibrate; a plurality of second plate springs, with an upper end portion of each of the plurality of second plate springs being secured to the working mass member; a single opposing mass member, with a lower end portion of each of the plurality of second plate springs being connected to the single opposing mass member; a piezoelectric device bonded to at least one surface of each of the plurality of second plate springs; and alternating voltage applying means for applying alternating voltage to each piezoelectric device. In the piezoelectric driven type vibratory feeder, by applying the alternating voltage to each piezoelectric device, each of the plurality of second plate springs undergoes bending vibration, causing the working mass member to vibrate by the bending vibration, so that an object is transported on the working mass member.
By virtue of the above-described structure, it is possible to prevent a reaction force from being transmitted to the base without increasing the height of the entire vibratory feeder. In addition, it is possible to smoothly transport an object to be transported by uniformly and stably vibrating the working mass member without producing rotational motion that results in perturbation.
When the structure of the basic form is used, a total spring constant of the first plate springs may be sufficiently smaller than a total spring constant of the second plate springs, and each first plate spring may act as a vibration-proof spring.
When the structure of the basic form is used, each second plate spring may be disposed substantially perpendicular to an object transportation surface of the working mass member.
When the structure of the basic form is used, each first plate spring may be disposed so as to be tilted at a predetermined angle from a direction in which the object is transported.
When the structure of the basic form is used, the piezoelectric driven type vibratory feeder may further comprise vibration detecting means for detecting any one of vibration displacement, velocity, and acceleration of either the working mass member or the opposing mass member; and alternating frequency controlling means for controlling a frequency of the alternating voltage applied to each piezoelectric device so that the working mass member undergoes resonant vibration at a natural frequency determined by masses of the working mass member and the opposing mass member and a spring constant of the second plate springs. By this, it is possible to ensure realization of a resonance condition. The vibration detecting means may be a proximity sensor disposed near one of the first plate springs or one of the second plate springs.
When the structure of the basic form is used, each of the plurality of first plate springs and each of the plurality of second plate springs may form a pair of front and back plate springs. When each of the plurality of first plate springs and each of the plurality of second plate springs form a pair of front and back plate springs, the working mass member may be a linear trough.
When the structure of the basic form is used, the plurality of first plate springs may be disposed at equiangular intervals, the plurality of second plate springs may be disposed at equiangular intervals, the working mass member may be supported so as to be capable of undergoing torsional vibration, and, by the torsional vibration of the working mass member, the object may be transported on the working mass member. When the plurality of first plate springs are disposed at equiangular intervals, the plurality of second plate springs are disposed at equiangular intervals, the working mass member is supported so as to be capable of undergoing torsional vibration, and, by the torsional vibration of the working mass member, the object is transported on the working mass member, the working mass member may be a bowl-shaped container with a spiral track.
When the structure of the basic form is used, each second plate spring may have a shape formed by bending a portion thereof substantially perpendicularly, and each second plate spring may include a substantially vertical portion and a substantially parallel portion with respect to an object transportation surface of the working mass member, with each substantially parallel portion being secured to a bottom surface of the working mass member. According to such a structure, since each substantially parallel portion is also deformed by being deflected and acts as an effective portion of its corresponding plate spring, the effective length of each second plate spring is increased. By this, it is possible to increase the displacement of each second plate spring, and to increase transportation capability of the feeder without increasing the height of the feeder. Here, to the extent allowed by its relationship with each member in the vicinity thereof, it is preferable to make the ratio of the length of each substantially horizontal portion to the length of each substantially vertical portion large. As this ratio becomes large, the effective length of each second plate spring is increased, and the spring constant of each second plate spring becomes small. Therefore, it is easier for each second plate spring to be displaced by a large amount.
When each second plate spring has a shape formed by bending a portion thereof substantially perpendicularly, and each second plate spring includes a substantially vertical portion and a substantially parallel portion with respect to an object transportation surface of the working mass member, with each substantially parallel portion being secured to a bottom surface of the working mass member, each piezoelectric device may be bonded to only a side opposite to the working mass member with respect to an inflection point of each second plate spring. When the effective length of each second plate spring becomes large, the inflection point of each second plate spring is displaced towards the working mass member from the center of its substantially vertical portion. Therefore, the proportion of a portion to which each piezoelectric device can be bonded becomes large.
When each second plate spring has a shape formed by bending a portion thereof substantially perpendicularly, and each second plate spring includes a substantially vertical portion and a substantially parallel portion with respect to an object transportation surface of the working mass member, with each substantially parallel portion being secured to a bottom surface of the working mass member, the piezoelectric driven type vibratory feeder may further comprise spring constant adjusting means for adjusting a spring constant of each second plate spring. When the piezoelectric driven type vibratory feeder further comprises spring constant adjusting means for adjusting a spring constant of each second plate spring, the spring constant adjusting means may comprise a spacer and a spring presser plate, and may change an effective length of each second plate spring at at least one of a working-mass-member side and an opposing-mass-member side. When the piezoelectric driven type vibratory feeder further comprises spring constant adjusting means for adjusting a spring constant of each second plate spring, the spring constant adjusting means may be constructed so as to make variable a position of securing the opposing mass member to each second plate spring by a slot formed in an end portion of each second plate spring.